Thank you for your question regarding CMS506v6 Safe Use of Opioids - Concurrent Prescribing. Please see below for answers to your questions:  1) What is the definition of the Admission Date/Time? The meaning is dependent on the measure’s expressed QDM datatype and timing attribute. Please refer to the Quality Data Model (QDM) guide for more information ( https://ecqi.healthit.gov/sites/default/files/QDM-v5.6-508.pdf ). For example, the “Encounter, Performed” datatype used in CMS506v6 logic utilizes the relevantPeriod timing attribute, in which the interval’s startTime is the time the encounter began (see page 33 in the guide).  2) What determines the Admission Date/Time? Is it the "arrival date/time", "ED room assignment date/time", "observation order date/time" or "inpatient order date/time"? The measure’s expression determines the applicability. For the Initial Population/Denominator and Numerator expressions the logic uses "InpatientHospitalEncounter.relevantPeriod". The start date and time for this encounter type is the time the encounter began (i.e., admission time). For the Denominator Exclusion, the logic uses the Global “HospitalizationWithObservation” function, which calculates the earliest starting point as the start of either the ED visit or observation stay. This function captures time spent in the ED and/or Observation for a patient that is subsequently admitted to inpatient, as long as the transition between the ED and/or Observation encounter(s) and the Inpatient encounter are equal to 1 hour or less. Therefore, Global "HospitalizationWithObservation" function is referencing those visits that qualify for the "Encounter Inpatient" value set and incorporates qualified time spent in the ED and/or Observation. For questions and issues related to the development and implementation of the CQL standard, please submit a ticket to the CQL Issue Tracker: https://oncprojectracking.healthit.gov/support/projects/CQLIT .